The invention relates to a water heater capable of preventing a water tube and the like of a heat exchanger from being frozen in a cold season, on a cold day, at a cold time (hereinafter referred to as a cold time).
In the case where a water heater unit having a heat source by combusting fuel gas is installed indoors, an exhaust gas is discharged outdoors using an exhaust tube which is provided with a backwind stopper for blocking off the entrance of an external backwind. At a cold time, the backwind stopper functions to prevent the water tube and the like provided around the heat exchanger from being frozen, and hence a heater is disposed on the water tube for preventing it from being frozen. A conventional antifreezing technique is disposed, for example in Japanese Patent Publication No. 6-80375, Japanese Patent Laid-Open Publication No. 10-47655, Japanese Patent No. 2, 897, 393, and Japanese Patent Laid-Open Publication No. 8-313066, and the like.
Meanwhile, it is not allowed to provide a backwind stopper on an exhaust tube in U.S.A., and hence a cold air caused by a backwind enters a heat exchanger at a cold time to cool down the heat exchanger, thereby producing freezing in the water tube. Even if the water tube is heated by heat of a heater installed on the water tube, freezing cannot be prevented in areas where an outside air temperature is extremely low.
Accordingly, it is an object of the invention to provide a water heater unit capable of preventing a water tube and the like of a heat exchanger without providing a backwind stopper on an exhaust tube.
To achieve the above object, the water heater unit according to a first aspect of the invention comprises combustion means for combusting fuel, a combustion chamber incorporating the combustion means therein and having an exhaust port for guiding combusted exhaust air produced in the combustion chamber to outside air, a heat exchanger provided with a water tube through which water flows and heating water which flows through the water tube by heat produced by combustion in the combustion means, temperature sensors attached to the water tube connected to the heat exchanger for detecting temperatures of the water tube, and an air supply fan for supplying air to the combustion chamber in which the combustion means is installed, characterized in that the air supply fan is driven to supply air to the combustion chamber when the temperatures detected by the temperature sensors reach a temperature at which freezing of water inside the water tube of the heat exchanger is expected, and the air from the combustion chamber is discharged toward the exhaust port so that the exhaust air warms the water tube.
The water heater unit according to a second aspect of the invention is characterized in that the first aspect of the invention further comprises a heater installed on the water tube of the heat exchanger for heating the water tube, wherein the heater is energized to heat the water tube when the temperatures detected by the temperature sensors reach a temperature at which freezing of water inside the water tube of the heat exchanger is expected.
The water heater unit according to a third aspect of the invention is characterized in that in the first aspect of the invention an outlet side water temperature of the water tube detected by the water temperature sensor of the first aspect of the invention is lower than the temperature of inlet side water temperature of the water tube detected by the water temperature sensor, the air supply fan is rotated.
The water heater unit according to a fourth aspect of the invention is characterized in that the first aspect of the invention further comprises a heater installed on the water tube of the heat exchanger for heating the water tube, and a wind pressure sensor installed at a part capable of detecting a backwind which enters the exhaust port, wherein when the wind pressure sensor detects a backwind exceeding a prescribed value, the air supply fan is stopped and the heater is energized so as to heat the water tube.
The water heater unit according to a fifth aspect of the invention is characterized in that in the first aspect of the invention the speed of rotation of the air supply fan of the first aspect of the invention is increased or decreased in response to the magnitude of a backwind which flows into an exhaust path through the exhaust port.
The water heater unit according to a sixth aspect of the invention is characterized in that the first aspect of the invention further comprises an air sensor installed on a part capable of detecting the volume of air which flows into the combustion chamber wherein the volume of air detected by the air sensor is controlled to be equal to a set volume of air by increasing or decreasing the speed of rotation of the air supply fan in response to the volume of air detected by the air sensor.
The water heater unit according to a seventh aspect of the invention is characterized in that the first aspect of the invention further comprises an air sensor installed on a part capable of detecting the volume of air which flows into the combustion chamber wherein the volume of air detected by the air sensor is controlled to be equal to a set volume of air by increasing or decreasing the speed of rotation of the air supply fan in response to the volume of air detected by the air sensor and the temperatures detected by the temperature sensors.
The water heater unit according to an eighth aspect of the invention is characterized in that in the first aspect of the invention the speed of rotation of air supply fan of the first aspect of the invention is increased or decreased in response to the temperatures detected by the temperature sensors.
The water heater unit according to a ninth aspect of the invention is characterized in that the first aspect of the invention further comprises differential pressure detection means installed on a part capable of detecting the difference of pressures between the interior of the housing of the water heater unit and the suction part of the air supply fan, wherein the speed of rotation of the air supply fan is controlled in a manner that the difference of pressures detected by the differential pressure detection means is equal to a predetermined difference of pressures.
The water heater unit according to a tenth aspect of the invention is characterized in that the first aspect of the invention further comprises differential pressure detection means installed on a part capable of detecting the difference of pressures between the interior of the housing of the water heater unit and the suction part of the air supply fan, wherein the speed of rotation of the air supply fan is controlled in a manner that the difference of pressures detected by the differential pressure detection means is equal to a predetermined difference of pressures in response to the difference of pressures detected by the differential pressure detection means and temperatures detected by the temperature sensors.
The water heater unit according to the eleventh aspect of the invention is characterized in that in the first aspect of the invention a load applied to exhaust air is discriminated by a driving current value while a driving voltage of a motor for driving the air supply fan and the speed of rotation of the air supply fan are respectively held constant, and wherein the speed of rotation of the air supply fan is controlled in a manner that it reaches a set current value in response to the load applied to the exhaust air.
The water heater unit according to the twelfth aspect of the invention is characterized in that in the first aspect of the invention a load applied to exhaust air is discriminated by a driving current value while a driving voltage of a motor for driving the air supply fan and the speed of rotation of the air supply fan are respectively constant, and wherein the speed of rotation of the air supply fan is controlled in a manner that it reaches a set current value in response to the load applied to the exhaust air and temperatures detected by the temperature sensors.
The water heater unit according to the thirteenth aspect of the invention is characterized in that in the second aspect of the invention the heater heats water inside the water tube when the temperature detected by the temperature sensor for detecting inlet side water temperature reaches close to a freezing temperature.
The water heater unit according to the fourteenth aspect of the invention is characterized in that in the fourth aspect of the invention the wind pressure sensor is attached to the combustion chamber while intervening a detection member.
The water heater unit according to the fifteenth aspect of the invention is characterized in that in the sixth aspect of the invention the air sensor is installed on a bypass provided between an upstream side and a downstream side of the combustion chamber.
The water heater unit according to the sixteenth aspect of the invention is characterized in that in the seventh aspect of the invention the air sensor is installed on a bypass provided between an upstream side and a downstream side of the combustion chamber.
The water heater unit according to the seventeenth aspect of the invention is characterized in that in the ninth aspect of the invention the differential pressure detection means is installed between the interior of the housing of the water heater unit and the suction part of the air supply fan.
The water heater unit according to the eighteenth aspect of the invention is characterized in that in the tenth aspect of the invention the differential pressure detection means is installed between the interior of the housing of the water heater unit and the suction part of the air supply fan.
With the construction of the water heater unit of the invention, if the freezing of water is expected at a cold time, the water tube is heated by a heater to introduce an indoor air into the combustion chamber of the heat exchanger so as to exhaust the indoor air through the exhaust port so that it can function as a substantial backwind stopper, thereby preventing the water tube from being frozen.
The objects, characteristics, effects and the like of the invention become clearer with reference to the following first to fifth embodiments of the invention, the detail description of the invention and the attached drawings.